1. Field of the Invention
The present invention relates to a magnetic field sensor having a magnetoresistance bridge. It can be used in the measurement of magnetic fields, particularly weak fields, i.e. of a few dozen Oersteds.
2. Discussion of the Background
Field sensors are known formed by four magnetoresistances connected as a WHEATSTONE bridge. FIG. 1 shows an example thereof. Each of the four magnetoresistances is shaped like an elongated bar and are pairwise connected in electrical opposition in the bridge (respectively R1 and R2), terminals being respectively located between the magnetoresistances. The input or supply voltage applied between two terminals of the bridge is designated Ve and the output or measuring voltage between the two other terminals is designated Vs.
In such a connection, only two of the magnetoresistances have to be sensitive to the magnetic field to be measured (e.g. the magnetoresistances R2), otherwise the bridge would be balanced in all circumstances. One of the solutions consists of placing a magnetic shield in front of two of the magnetoresistances, namely the magnetoresistances R1 in FIG. 2, where the shield carries the reference Ec.
Such a sensor is e.g. described in the article by J. DAUGHTON et al entitled "Magnetic Field Sensors Using GMR Multilayer", published in "IEEE Trans on Magnetics", vol. 30, No. 2, March 1994.
Although satisfactory in certain respects, such sensors remain complex due to the means intended to render passive two of the magnetoresistances,